Structured Diamond Tool Made by Focused Ion Beam Nanomachining

ABSTRACT

A structured diamond tool having a predefined grayscale grating profile shape allows a corresponding grayscale grating profile to be machined into a work piece with a single pass with high accuracy. Manufacture of grayscale gratings using this technique saves time compared to the situation where the profile is machined by a single-point diamond tool with multiple passes. Also, more time-saving is realized if more than one period is machined in the diamond tool. Such a tool can be manufactured using a high precision focused ion beam (FIB), which is a true nanomachining tool that can machine features on the order of tens of nanometers. The diamond tool made by FIB therefore has extremely fine resolution and features required by the grayscale grating.

FIELD OF THE INVENTION

The present invention generally relates to manufacture of grayscalegratings, and relates in particular to a structured diamond tool havinga grayscale grating profile shape formed by a high intensity focused ionbeam.

BACKGROUND OF THE INVENTION

Optical pickups in CD, DVD, and newer BD drives have gratings (calledholographic optical elements, HOES) in them to diffract the laser beamfor various purposes, such as focus tracking and signal detection. Thegratings can be straight to diffract an incident beam into severalorders, or curved to have additional functions other than splitting thebeams, such as focusing the beams to the detectors.

One way of mass producing the gratings is to make a mold first, andmanufacture the gratings by press molding. For binary gratings,photolithographic processes have been used to make the grating molds.However, as the grating design evolves from binary to grayscale(blazed), and the grating period becomes smaller for shorterwavelengths, photolithographic processes become less suitable forproducing the required grating molds.

It is known that single point diamond turning can be used to machinegratings and grating molds. In the known process, the diamond tool has asingle sharp tip. The diamond tool makes one or more ruling passeswithin one period to remove material to fabricate the grating or gratingmold. This process works well for simple grating shapes.

Advanced grating designs for optical pickup can require more complicatedgrating profiles within one period to achieve desired functions of thegrating. As an example, a particular design for an optical pickupgrating has the following shape shown in FIG. 1. Such gratings havefine, micrometer- to sub-micrometer-size features that are difficult tomachine with a simple, single-point diamond tool. What is needed is away to make structured diamond tools that can machine gratings orgrating molds with complicated shapes. The present invention fulfillsthis need.

SUMMARY OF THE INVENTION

In accordance with the present invention, a structured diamond toolhaving a predefined grayscale grating profile shape allows acorresponding grayscale profile to be machined into a work piece with asingle pass with high accuracy. Manufacture of grayscale gratings usingsuch a structured diamond tool saves time compared to the situationwhere the profile is machined by a single-point diamond tool withmultiple passes. Also, more time-saving is realized if more than oneperiod is machined in the diamond tool. Such a tool is manufacturedusing a high precision focused ion beam (FIB), which is a truenanomachining tool that can machine features on the order of tens ofnanometers. The diamond tool made by FIB therefore has extremely fineresolution and features required by the grayscale grating.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a two-dimensional graph illustrating a grayscale gratingprofile in accordance with the present invention, wherein the abscissaand ordinate axes are both in micrometer units;

FIG. 2 is a set of views illustrating viewing of a tip of a diamondtool, including a three-dimensional overview in FIG. 2A, a magnified topview in FIG. 2B, and a top view of the diamond tool tip as viewed in aview mode of an FIB machine at zero degrees tilt and twenty-fivethousand times magnification, with a scale bar at five micrometers;

FIG. 3 is a view illustrating a predefined grayscale grating profileshape overlaying the magnified FIB image of FIG. 2C in accordance withthe present invention;

FIG. 4 is a view illustrating an end product structured diamond toolmanufactured in accordance with the present invention as viewed in aview mode of an FIB machine at fifty-thousand times magnification, witha scale bar at 2 micrometers;

FIG. 5 is a top view illustrating a workpiece cut by repetitiveapplication of the structured diamond tool to obtain straight grooves;

FIG. 6 is a side view illustrating a workpiece cut by repetitiveapplication of the structured diamond tool; and

FIG. 7 is a top view illustrating a workpiece cut by repetitiveapplication of the structured diamond tool to obtain curved grooves.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

The present invention uses high precision focused ion beam (FIB)nanomachining to machine the profile of at least one period of thegrating in the tip of a diamond tool. FIG. 1 illustrates one period ofan example grayscale grating profile. It has individual features lessthan one-tenth of a micrometer high and less than one quartermicrometers wide. A single period composed of such features can bethree-tenths of a micrometer or less in height, and less than fourmicrometers wide. Accordingly, a predefined grayscale grating profilemachined into a tip of the diamond tool bears features on an order oftens of nanometers.

If the diamond tool is used to machine the grating directly, then thenegative of the grating profile shape is made into the diamond tool. Ifthe diamond tool is used to machine the grating mold, then the normalgrating shape is made into the diamond tool. In diamond machining, thestructured diamond tool cuts into the substrate material (either thegrating material itself or the mold material) with a depth at least themaximum depth of the designed grating shape. The diamond tool is ruledalong the grating groove. For the structured diamond tool that has n(n≧1) periods of the grating profiles, n grooves are made after eachruling along the groove. The diamond tool is then stepped n periods inthe direction perpendicular to the grating groove, and the machiningprocess is repeated.

The process of FIB nanomachining of a structured diamond tool proceedsas follows. Start with a single point diamond tool, as shown is FIG. 2(a) (3D view) and FIG. 2B (top view). Place the diamond tool in an FIBmachine. Using the FIB machine's view mode (low current), the diamondtip is viewed by the operator, as shown in FIG. 2C (top view). The FIBmachine's ion beam comes into the view; that is, it strikes the imageshown in FIG. 2C in the normal direction with respect to a plane of theimage. In other words, the ion beam is orthogonal to a plane in whichlies a top surface 200 (FIG. 2A) of the diamond tip. The FIBmagnification is calibrated so that the correct size of the diamond toolis shown in the image, as the size bar 202 in the lower part in FIG. 2Cindicates.

Using the FIB machine drawing software, overlay the grating profile 300to be made over the image of the diamond tip, as shown in FIG. 3. Thedrawing software draws the correct size according to the magnificationof the image, so the overlaid image has the correct size of the gratingprofile.

Machine the diamond tool with FIB along the overlaid profile. The ionbeam strikes a bottom surface of the diamond tool at normal incidence asdescribed above. Cut through to complete the diamond tool. The resultingstructured diamond tool 400 is shown in FIG. 4.

The diamond machining of the grating grooves either for making thegrating directly or making the mold is shown in FIG. 5 and FIG. 6. FIG.5 is the top view of the work piece 502. FIG. 6 is a set of the crosssection views of the work piece 502 showing the grayscale gratingprofile made in the work piece as it is machined by the structureddiamond tool 400. A first groove 500 is made by cutting the work piece502 with the diamond in the grooving direction 504. The diamond tool 400is then stepped in a direction perpendicular to the grooving direction504 according to a pitch between grooves 506. Then a second groove 508is cut by the structured diamond tool. This process is repeated until afinal groove 510 is cut. It should be noted that if the structureddiamond tool has n periods of the grating profile, the step size 506 inthe direction perpendicular to the grooves is n periods of the grating.The cut depth, as shown in FIG. 6, should be at least equal to orgreater than the maximum height of the grating profile.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. For example, FIG. 5shows straight grating grooves, however, it is important to note thatthe grooves do not have to be straight. Turning now to FIG. 7, curvedgrating grooves can be made as well. In this case, the workpiece 502and/or the structured diamond tool 400 can be rotated in order to keepthe normal of a diamond tool rake face aligned with the tangents ofcurves 500 and 508. Such variations are not to be regarded as adeparture from the spirit and scope of the invention.

1. A process of manufacturing a structured diamond tool for use inmanufacture of grayscale gratings, the method comprising: placing adiamond tool in a focused ion beam (FIB) machine; employing FIB machinedrawing software to overlay an image of a tip of the diamond tool with ashape corresponding to at least one of: (a) a predefined grayscalegrating profile; or (b) a negative of a predefined grayscale gratingprofile; machining the diamond tool with FIB along the shape overlayingthe image of the tip.
 2. The process of claim 1, further comprisingusing a view mode of the FIB machine to view the tip of the diamondtool.
 3. The process of claim 2, further comprising calibratingmagnification of the FIB machine so that the image of the tip of thediamond tool is shown at a predetermined size;
 4. The process of claim1, further comprising cutting through the diamond tool to complete thestructured diamond tool.
 5. A method of manufacturing a grayscalegrating, comprising: machining a work piece using a structured diamondtool having a predefined grayscale grating profile shape.
 6. The methodof claim 5, wherein the predefined grayscale grating profile shape is anegative shape of a corresponding grating profile, the method furthercomprising designating the work piece as the grating.
 7. The method ofclaim 5, further comprising employing the work piece as a mold to makethe grating.
 8. The method of claim 5, further comprising simultaneouslymachining multiple periods of the grating profile in the work piece bymachining the work piece surface with the tool, wherein the tool hasmultiple periods of the predefined grayscale grating profile shape. 9.The method of claim 5, further comprising: cutting a first groove in thework piece with the structured diamond tool in a grooving direction;stepping the structured diamond tool in a direction perpendicular to thegrooving direction according to a pitch between grooves; and cutting asecond groove in the work piece with the structured diamond tool in thegrooving direction.
 10. The method of claim 9, wherein the structureddiamond tool has n periods of a grating profile corresponding to exactlyone of the grating profile shape or a negative of the grating profileshape, and a step size for stepping in the direction perpendicular tothe grooving direction is n periods of the grating profile.
 11. Themethod of claim 9, wherein a cut depth for cutting the first groove andthe second groove is at least equal to or greater than a maximum heightof the grating profile shape.
 12. The method of claim 9, furthercomprising rotating at least one of the workpiece or the structureddiamond tool in order to keep a normal of a rake face of the structureddiamond tool aligned with a tangent of a curve, thereby cutting a curvedgroove.
 13. A structured diamond tool for use in manufacture of agrayscale grating, comprising: a predefined grayscale grating profilemachined into a tip of the diamond tool and bearing features on an orderof tens of nanometers.
 14. A structured diamond tool for use inmanufacture of a mold for a grayscale grating, comprising: a negative ofa predefined grayscale grating profile shape machined into a tip of thediamond tool and bearing features on an order of tens of nanometers. 15.A process for milling a work piece with a structured diamond tool, theprocess comprising: making a first groove in the work piece by cuttingthe work piece with the structured diamond tool in a first direction;stepping the diamond tool in a second direction perpendicular to thefirst direction; making a second groove in the work piece by cutting thework piece with the structured diamond tool in one of the firstdirection or a third direction parallel to the first direction.
 16. Themethod of claim 15, wherein the structured diamond tool has n periods ofa grating profile having one or more design features of five nanometersto ten nanometers in size.
 17. The method of claim 15, wherein a stepsize in the second direction is equal to n periods of the gratingprofile.
 18. The method of claim 15, wherein a cut depth used to makegrooves is at least equal to or greater than a maximum height of thegrating profile measured from a lowest point of the grating profilewithin the n periods to a highest point of the grating profile withinthe n periods.
 19. The method of claim 15, further comprising rotatingat least one of the workpiece or the structured diamond tool in order tokeep a normal of a rake face of the structured diamond tool aligned witha tangent of a curve, thereby cutting a curved groove.
 20. A method ofmanufacturing a grayscale grating, comprising: selecting a grayscalegrating profile; employing a focused ion beam (FIB) machine tomanufacture a structured diamond tool having a grayscale grating profileshape corresponding to exactly one of: (a) one or more the grayscalegrating profile; or (b) a negative of the grayscale grating profile; andusing the structured diamond tool to manufacture the grayscale grating.21. The method of claim 20, further comprising placing a diamond tool inthe FIB machine.
 22. The method of claim 20, further comprising using aview mode of the FIB machine to view a tip of a diamond tool.
 23. Themethod of claim 20, further comprising calibrating magnification of theFIB machine so that an image of a tip of a diamond tool is shown at apredetermined size.
 24. The method of claim 20, further comprisingemploying drawing software of the FIB machine to overlay an image of atip of a diamond tool with an image of the grayscale grating profileshape.
 25. The method of claim 20, further comprising machining adiamond tool with FIB along an image of the grayscale grating profileshape overlaying an image of a tip of a diamond tool.
 26. The method ofclaim 20, further comprising cutting through a diamond tool to completethe structured diamond tool.
 27. The method of claim 20, furthercomprising machining a work piece surface using the structured diamondtool.
 28. The method of claim 27, wherein the predefined grayscalegrating profile shape is a negative shape of a corresponding gratingprofile, the method further comprising designating the work piece as thegrating.
 29. The method of claim 27, further comprising employing thework piece as a mold to make the grating.
 30. The method of claim 27,further comprising simultaneously machining multiple periods of thegrating profile in the work piece by machining the work piece surfacewith the tool, wherein the tool has multiple periods of the predefinedgrayscale grating profile shape.
 31. The method of claim 27, furthercomprising: cutting a first groove in the work piece with the structureddiamond tool in a grooving direction; stepping the structured diamondtool in a direction perpendicular to the grooving direction according toa pitch between grooves; and cutting a second groove in the work piecewith the structured diamond tool in the grooving direction.
 32. Themethod of claim 31, wherein the structured diamond tool has n periods ofa grating profile corresponding to exactly one of the grating profileshape or a negative of the grating profile shape, and a step size forstepping in the direction perpendicular to the grooving direction is nperiods of the grating profile.
 33. The method of claim 31, wherein acut depth for cutting the first groove and the second groove is at leastequal to or greater than a maximum height of the grating profile shape.34. The method of claim 31, further comprising rotating at least one ofthe workpiece or the structured diamond tool in order to keep a normalof a rake face of the structured diamond tool aligned with a tangent ofa curve, thereby cutting a curved groove.